The contents of an enclosure such as a shipping container or storage locker are often susceptible to theft or damage from mishandling. In many cases, no obvious evidence of the theft or damage can be seen by inspecting the enclosure or its contents. A thief might be sophisticated enough to remove only a small number of valuable items from a package and then reseal it, making it appear that the package was not disturbed. In many cases, the shipper and receiver of such packages are unwilling to make a thorough enough inventory and inspection to detect such pilferage. Many times, the missing valuable items are attributed to a miscount of the product before it was shipped from the manufacturer, leaving the manufacturer to bear the cost of the theft.
Damage from mishandling is also difficult to detect, especially with fragile shipping contents. A package might be dropped off of a loading dock, causing breakage of items that are inside smaller packages. The damage will not be evident until the end user of the fragile product opens the smaller package. At this point, it is more difficult to determine who is responsible for the breakage.
Some products that would be shipped or stored in an enclosure are vulnerable to environmental conditions such as temperature extremes, excessive humidity, and magnetic fields. These products include sensitive electronic devices, magnetic media, and living organisms. When such products are shipped or stored, the environment in which the package containing them has been placed must be controlled. Even if no theft or breakage has occurred, such products can be damaged by remaining too long in a particularly hot or cold area or passing through a magnetic field. There is no way to easily determine if such damage has occurred by inspecting the package.
Electronic devices are described in the patent literature that detect unwanted access to a container by monitoring some sort of physical connection to the container. U.S. Pat. No. 5,189,396, issued to Stobbe on Feb. 23, 1993, for example, calls for a loop of wire or optical fiber to be engaged with the container so that it will be broken if the container is opened. U.S. Pat. No. 5,615,247, issued to Mills on Mar. 15, 1997, describes a pair of cables that are threaded through the door handles of a cargo transport container. These devices detect unwanted access to the container by a disruption of the physical connection to it.
These devices cannot easily be made inconspicuous because they require a physical connection that will be disrupted if the container is opened. The '247 patent teaches away from making the monitoring device inconspicuous by specifying a rotating pattern of lights on the cables. The disclosure of U.S. Pat. No. 4,750,197, issued to Denekamp et al. on Jun. 7, 1988, acknowledges the conspicuousness of an electronic monitoring device using a sensor physically attached to the container. This patent teaches a system including both active and decoy monitoring systems, specifically designed to overcome the fact that each of the monitoring devices is readily apparent to personnel accessing the container.
Applicant has found that a more compact detection device would be desirable because it would not easily be noticed by someone who would tamper with the contents of a shipping or storage enclosure into which it has been placed. A smaller device would be desirable for many other reasons even if concealment were not the objective. A compact detection device would add less to the size and weight of a package in which it is placed for shipping. If the device were used to detect temperature extremes, it could do so faster and more accurately because it would have less thermal mass. A compact device used to measure acceleration or shock would add less mass to the physical system on which it is mounted, and would thus tend not to affect the measurement as much. A smaller device would cost less to manufacture as well.
Compact indicator devices are available that change their physical state to show whether the package to which they are affixed has been subjected to an undesirable environmental condition. These devices undergo some irreversible chemical reaction or mechanical operation when subjected to disposition that could damage the contents of the package to which they are affixed. Such disposition includes excessive humidity, temperature that is too high or too low, angular displacement from vertical, and excessive shock.
These passive devices require specific mechanical or chemical compositions that are especially formulated for the type and severity of the environmental stress to be detected. They are not programmable for specific types and severity of stress. This complicates manufacturing and inventory if a broad range of requirements is to be met. The mechanical deformations and chemical reactions are often not reversible, so the devices must usually be disposed of after use. Cost and limited availability of chemical compositions may be significant as well.
These devices are limited in the amount of information that they can provide about such unwanted disposition because of their simple state-changing mode of operation. A simple pass/fail indicator shows that environmental stress has occurred, but it does not give any more information about the environmental stress. More information is often useful to estimate the extent of damage or to identify the responsible party. If several parties are involved in the shipping of a damaged package, for example, the responsible party cannot be identified without knowing when the damage occurred. Such information could include the severity of the environmental stress as well as the time and date of its occurrence. It might also be useful to know the frequency and duration of stressful events. None of these details can be recorded with a passive state-changing indicator.
Accordingly, it would be advantageous to provide a compact, self-contained device that could detect and record information about unwanted disposition of the contents of an enclosure. It would be desirable for device to record information more detailed than that provided by a passive indicator device in spite of its small size. It would also be desirable for such a device to communicate the information in a format compatible with its compact form.